Nitrous oxide emissions from wheat fields: N source, N rate, irrigation, and weather effects

Nitrous oxide (N 2 O) is a potent greenhouse gas and a major ozone-depleting substance, mainly produced from agricultural soils. Enhanced-efficiency nitrogen fertilizers (EEFs) are designed to improve nitrogen-use efficiency (NUE) of crops, and reduce losses associated with N 2 O emissions. This study evaluated five EEFs, including nitrification inhibitor (NI), urease inhibitor (UI), two dual inhibitors containing both NI and UI (DIS and DID), and polymer-coated urea (PCU), applied at seeding of spring wheat ( Triticum aestivum L.) with N rates of 120, 180, and 240 kg urea-N ha −1 under irrigation and rainfed, encompassing 13 site-years in Alberta, Canada. Baseline N 2 O emission comparisons included untreated urea and a no urea control. Treatments containing nitrification inhibitors (NI, DIS, and DID) reduced both area- and yield-based N 2 O emissions compared to untreated urea, with more consistent effects under irrigation. The N 2 O emissions from rainfed systems were inconsistent across experimental years as driven by weather variability. Conversely, PCU and UI did not reduce emissions in rainfed or irrigated systems; instead, higher N 2 O emissions were observed compared to untreated urea, with PCU also leaving elevated residual soil nitrate post-harvest (31.1 ± 6.2 mg N kg −1 soil). Across N rates, emission factors were highest at 240 kg N ha −1 , while NUE of wheat crops was highest at 120 kg N ha −1 rate. Results suggest that using nitrification inhibitors combined with an N rate of 120 kg N ha −1 is a promising strategy to mitigate N 2 O emissions and improve nitrogen management. These findings offer practical guidance for producers and policy-makers in regions with comparable soil and environmental conditions globally.